1. Field of the Invention
The invention relates to a safety arrangement for a manually guided soil compaction roller.
2. Description of the Related Art
In such soil compaction rollers, in particular rollers which are run with an operator in attendance, the operator walks behind the roller and controls it via a handle, which is fastened to a pole and has a travel lever for setting the travel speed and direction. The roller is normally moved via a hydraulic unit in forward direction and reverse direction, that is toward the operator.
A safety arrangement, often also referred to as dead man""s circuit, serves in such soil compaction rollers to switch off the propulsion of the roller if the roller moves backward, i.e. in the direction of the operator guiding the roller, and the operator himself can no longer move backward or cannot escape from the roller. This problem may occur, for example, if the operator walks backward with the roller into an obstacle, gets into a panic and consequently forgets to stop the roller or move it in the opposite direction.
An actuator which is able to register the fact that the roller runs against an obstacle, for example the operator, is therefore provided in known safety arrangements. To this end, the safety arrangements have an actuator which is displaceable between an operating position and a hazard position and, if the operator comes into contact with it, is displaceable out of the operating position into the hazard position and consequently stops the roller.
To this end, it is stipulated in standards that, after the response of the safety device, the stopping travel of the roller must be smaller than the remaining operating travel of the actuator after the roller is switched off in order to avoid squeezing the operator.
DE-A 41 29 915 A1 discloses a safety arrangement in which the travel speed and direction can be set via a travel lever. The roller is guided via an additional handle, which is vertically pivotable like a lever and can be pivoted from an upswung basic position down into a working position in which its free end is still clearly above the horizontal established by its pivot. The travel lever, otherwise held in neutral position by spring loading, is fixed in the desired deflected position in a positive-locking manner by swinging down the handle. When the handle is swung up, which is effected automatically, for example, if the handle comes into contact with an obstacle, the positive-locking connection is neutralized, as a result of which the travel lever moves into the neutral position in a spring-loaded manner and stops the roller. Movement of the roller in the opposite direction is possible by further actuation of the travel lever.
In such solutions, it is always possible to reach the neutral position or set the forward direction by actuation of the travel lever. In this case, it was assumed that the operator, upon coming into contact with an obstacle at the rear, releases the travel lever or that the holding force of the operator is less than the restoring force, initiated by the safety actuator, on the travel lever. However, it has been found that the holding force of the hand, in particular in a panic situation, can become enormous, so that the operator does not let go of the travel lever and, by further travel of the roller, a permitted maximum force of 230 newtons may be exceeded by the safety actuator in contact with the body of the operator. However, a higher loading than the admissible maximum force may alone result in considerable injuries to the operator.
In order to remove this problem, solutions in which, despite the force with which the operator takes a firm hold of the travel lever, a positive-locking connection between travel lever and the control line leading to the drive is unlocked by the safety actuator detecting the obstacle have been proposed. As a result, the spring-loaded control line jumps into the stop position. A disadvantage of this principle, however, is that the positive-locking connection between travel lever and control line can only be restored when the safety actuator displaced by the obstacle has again reached its initial or operating position, so that a coupling between travel lever and control line becomes possible again. Not until then is a movement of the roller in the opposite direction possible. To this end, however, the operator must have freed himself from his jammed position beforehand, since otherwise the safety actuator cannot be returned into the operating position.
The object of the invention is to specify a safety arrangement for a manually guided soil compaction roller, which safety arrangement, even if the operator frantically keeps a firm hold of the travel lever, permits reliable stopping of the roller and, on the other hand, permits forward travel of the roller away from the operator even if the safety arrangement has been triggered by travel of the roller against the operator.
According to the invention, the object is achieved by a safety arrangement having the features of patent claim 1. Advantageous developments of the invention can be gathered from the dependent claims.
In the safety arrangement according to the invention, in addition to the first coupling known per se, often designed as a jaw clutch, between a travel lever and an adjusting element connected to a control line, a second coupling is provided. The first coupling can be released by displacement of a safety actuator from an operating position into a hazard position. The second coupling, however, is retained even in this case, but can only transmit forces of the travel lever to the adjusting element if the travel lever is moved in the forward direction. This has the advantage that, if the roller runs into an obstacle and the safety actuator is actuated by the obstacle, e.g. the body of the operator, the first coupling is neutralized, as a result of which the adjusting element moves into neutral position in a spring-loaded manner and stops the roller. So that the operator can free himself from his emergency situation, he can put the travel lever, which at first is still in the reverse travel position, into the forward position. The movement of the travel lever in the forward direction is transmitted via the second coupling to the adjusting element and thus via the control line to the drive of the roller, so that the latter moves in the forward direction away from the operator and releases the latter.
The second coupling likewise preferably has a positive-locking clutch in which the adjusting element carries a driver, against which a stop provided on the travel lever can run. This ensures that forces can be transmitted only in one direction, namely the forward direction of the roller.